Master of Science, The Ohio State University, 2019, Aero/Astro Engineering

This thesis details aeroelastic response prediction of hoods on automobiles in the wake of a leading vehicle. Such conditions can lead to significant hood vibration due to the unsteady loads caused by vortex shedding. A primary focus is the sensitivity of the aeroelastic response to the aerodynamic modeling fidelity. This is assessed by considering both Reynolds-Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) flow models. The aeroelastic analysis is carried out by coupling a commercial computational Fluid dynamics (CFD) solver (StarCCM+) to a commercial computational structural dynamics (CSD) solver (Abaqus). Two different configurations are considered: 1) sedan-sedan and 2) sedan-SUV. This enables the consideration of both varied geometry and structural stiffness on the aeroelastic response. Comparisons between RANS and DES emphasize the importance of turbulence modeling fidelity in order to capture the unsteadiness of the flow and the vibration response of the hood. These comparisons include analysis of the lift forces, pressure loads on the hood, and Power Spectral Density Analysis (PSD) of the flow in the region between the two vehicles. As expected, DES predicts higher frequency content and significantly higher turbulence levels than RANS. Both the sedan and SUV hoods are sensitive to the turbulent fluctuations predicted by DES. The increased levels of turbulence result in up to 40 - 60% higher maximum peak to peak deformation and the excitation of a torsional mode of the hood for the sedan-sedan case. For the more flexible hood configuration (sedan - SUV), these differences are even higher, with maximum peak to peak deformations of up to 17 – 71% higher than the RANS solution.

Committee: Jack McNamara PhD (Advisor); Austin Kimbrell (Committee Member); Mei Zhuang PhD (Committee Member) Subjects: Aerospace Engineering; Automotive Engineering; Engineering

Master of Science, University of Toledo, 2014, Mechanical Engineering

Helicopters and other Vertical Take-Off or Landing (VTOL) vehicles exhibit an interesting combination of structural dynamic and aerodynamic phenomena which together drive the rotor performance. The combination of factors involved make simulating the rotor a challenging and multidisciplinary effort, and one which is still an active area of interest in the industry because of the money and time it could save during design. Modern tools allow the prediction of rotorcraft physics from first principles. Analysis of the rotor system with this level of accuracy provides the understanding necessary to improve its performance. There has historically been a divide between the comprehensive codes which perform aeroelastic rotor simulations using simplified aerodynamic models, and the very computationally intensive Navier-Stokes Computational Fluid Dynamics (CFD) solvers. As computer resources become more available, efforts have been made to replace the simplified aerodynamics of the comprehensive codes with the more accurate results from a CFD code. The objective of this work is to perform aeroelastic rotorcraft analysis using first-principles simulations for both fluids and structural predictions using tools available at the University of Toledo. Two separate codes are coupled together in both loose coupling (data exchange on a periodic interval) and tight coupling (data exchange each time step) schemes. To allow the coupling to be carried out in a reliable and efficient way, a Fluid-Structure Interaction code was developed which automatically performs primary functions of loose and tight coupling procedures. Flow phenomena such as transonics, dynamic stall, locally reversed flow on a blade, and Blade-Vortex Interaction (BVI) were simulated in this work. Results of the analysis show aerodynamic load improvement due to the inclusion of the CFD-based airloads in the structural dynamics analysis of the Computational Structural Dynamics (CSD) code. Improvements came (open full item for complete abstract)

Committee: Chunhua Sheng Ph.D. (Advisor); Abdeh Afjeh Ph.D. (Committee Member); Ray Hixon Ph.D. (Committee Member); Glenn Lipscomb Ph.D. (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science in Aerospace Systems Engineering (MSASE), Wright State University, 2024, Mechanical Engineering

The development of high order numerical schemes has been instrumental in advancing computational fluid dynamics (CFD), particularly for applications requiring high resolution of discontinuities and complex flow phenomena prevalent in high-speed flows. This thesis introduces the Pade-ENO scheme, a high-order method that integrates Essentially Non-Oscillatory (ENO) techniques with compact Pade stencils to achieve superior accuracy, up to 7th order, while maintaining stability in harsh environments. The scheme's performance is evaluated through benchmark tests, including the advection equation, Burgers' equation, and the Euler equations. For high Mach number flows, such as the sod shock tube the Pade-ENO method demonstrates its ability to resolve sharp gradients and discontinuities with no smoothing required. Numerical results highlight the scheme's robustness and its potential as a powerful tool for high-speed aerodynamic simulations, paving the way for future advancements in CFD modeling.

Committee: George Huang Ph.D., P.E. (Advisor); Jose Camberos Ph.D., P.E. (Committee Member); Nicholas Bisek Ph.D. (Committee Member); James Menart Ph.D. (Other) Subjects: Aerospace Engineering; Engineering; Fluid Dynamics; Mathematics; Mechanical Engineering

PhD, University of Cincinnati, 2024, Arts and Sciences: Mathematical Sciences

A cerebral or intracranial aneurysm, commonly referred to as a brain aneurysm, is a potentially life-threatening condition characterized by a bulge or ballooning in a blood vessel in the brain. This condition can affect individuals of any age and, if ruptured, can lead to hemorrhagic stroke, brain damage, and even death. The Brain Aneurysm Foundation reports that an estimated 6.8 million people in the United States have an unruptured brain aneurysm, with approximately 30,000 individuals experiencing a rupture each year. These ruptures have a high fatality rate, with 50% of cases being fatal and 66% of survivors experiencing lasting neurological impairments. Despite the risks, routine screening for brain aneurysms in healthy individuals is uncommon, and aneurysms are often discovered incidentally. Once it is identified, the decision to treat an aneurysm involves significant caution due to the complexity and risks of brain surgery. Hence, a thorough understanding of blood flow in the aneurysm region is essential for developing effective treatment plans. Current research has made strides in understanding aneurysm hemodynamics, mechanical modeling, and treatment devices like stents and coils. While these models offer insight, they often lack flexibility, focusing either on fixed, patient-specific geometries or oversimplified idealized structures that inadequately capture aneurysm dynamics. Recent computational advancements, including AI integration, have improved model accuracy and reduced simulation time, but inconsistencies across studies point to a need for more standardized frameworks. My PhD research addressed these gaps by developing a novel mathematical model that combines anatomical accuracy with flexibility, allowing for varied geometric properties while maintaining structural accuracy. This model aims to predict blood flow dynamics more effectively, supporting personalized aneurysm treatment planning and potentially improving clinical out (open full item for complete abstract)

Committee: Benjamin Vaughan Ph.D. (Committee Chair); Stephan Pelikan Ph.D. (Committee Member); Deniz Bilman Ph.D. (Committee Member) Subjects: Applied Mathematics

Master of Science (MS), Ohio University, 2024, Chemical Engineering (Engineering and Technology)

The objective of this research is to continue development of the flowtube, a new type of test equipment developed at the ICMT. Baseline testing is commonly used to validate models and ensure understanding of the electrochemical system. Baseline mass transfer experiments were performed using a rotating cylinder electrode (RCE). Baseline corrosion experiments were completed using an RCE as well as a rotating disk electrode (RDE). Mass transfer within the RDE system was also successfully modeled using computational fluid dynamics (CFD) software Ansys Fluent. Experimental and simulated results were validated using well known and accepted correlations. Validation of the CFD simulations is vital because no physical prototype for the flowtube currently exists to compare with the CFD results. The RDE simulations will serve as a baseline to prove that Fluent is capable of performing accurate mass transfer calculations and potentially future corrosion simulations. Current testing apparatuses for flowing environments tend to be large and/or difficult to use in a small-scale lab. To combat this, the flowtube cell can create a controlled single phase flow regime in a glass cell or autoclave and can test 3 samples at one time in its most recent revision. A new revision is currently being created, so the flowtube was modeled using CFD in order to determine how design alterations will affect the flowing environment within the glass cell. The flowtube hydrodynamics have been successfully modeled using Ansys Fluent. This model can illustrate fluid flow in the glass cell around the flowtube apparatus in both steady state and transient conditions. This model will continue to be expanded upon in the future to reflect the design considerations for the next prototype version. Design considerations and their impact on the hydrodynamics of the flowtube system were analyzed through this research.

Committee: Srdjan Nesic (Advisor); Marc Singer (Committee Member); Bruce Brown (Committee Member); Rebecca Barlag (Committee Member) Subjects: Chemical Engineering; Engineering; Fluid Dynamics

Master of Science (M.S.), University of Dayton, 2024, Aerospace Engineering

Traditional conceptual-level aerodynamic analysis is limited to empirical and/or inviscid models due to considerations of computational cost and complexity. There is a distinct desire to incorporate higher-fidelity analysis into the conceptual-design process as early as possible. This work seeks to enable the use of high-fidelity data by developing and applying multi-fidelity surrogate models that can efficiently predict the underlying response of a system with high accuracy. To that end, a novel form of the multi-fidelity polynomial chaos expansion (PCE) method is introduced, extending the surrogate modeling technique to accept three distinct fidelities of input. The PCE implementation is evaluated for a series of analytical test functions, showing excellent accuracy in creating multi-fidelity surrogate models. Aerodynamic analysis of a generic hypersonic vehicle (GHV) is performed using three codes of increasing fidelity: CBAERO (panel code), Cart3D (Euler), and FUN3D (RANS). The multi-fidelity PCE technique is used to model the aerodynamic responses of the GHV over a broad, five-dimensional input domain defined by Mach number, dynamic pressure, angle of attack, and left and right control surface settings. Mono-, bi-, and tri-fidelity PCE surrogates are generated and evaluated against a high-fidelity “truth” database to assess the global error of the surrogates focusing on the prediction of lift, drag, and pitching moment coefficients. Both monofidelity and multi-fidelity surrogates show excellent predictive capabilities. Multi-fidelity PCE models show significant promise, generating aerodynamic databases anchored to RANS fidelity at a fraction of the cost of direct evaluation.

Committee: Markus Rumpfkeil (Advisor); Jose Camberos (Committee Member); Timothy Eymann (Committee Member) Subjects: Aerospace Engineering

MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

Liquid-vapor phase change is a key to modeling countless multiphase flows, notably in the storage of cryogenic propellants during long-term space missions. Although recent studies have progressed our understanding of the physics of phase change, reliable models to compute the interphase mass transfer remain elusive, and popular phase change models rely heavily on tuning coefficients to model the phase change mass transfer. Large inconsistencies in the phase change calculations occur due to the unpredictable nature of these tuning coefficients. In this work, several pieces of the kinetic phase change mechanism are used from other studies to build a new computational routine capable of modeling kinetic phase change without the need for tuning parameters. A common problem with implementing kinetic phase change models is the need for values of the accommodation coefficient. This problem is solved by using a transition state theory-based model to compute the accommodation coefficient as a function of the liquid and vapor densities. Vapor temperature is found to play a critical role in the accurate prediction of phase change rates. Errors as large as one order of magnitude are seen for deviations as small as 0.1% in the values of the vapor temperature. Accurate modeling of phase change rates requires vapor temperature within the Knudsen layer to be used as inputs to the kinetic models. Due to the inability of macro-scale computational fluid dynamics (CFD) models to capture temperature gradients in the Knudsen layer, a new parameter, γ, is introduced to approximate the Knudsen layer vapor temperature. This new computational routine is implemented within Ansys Fluent™ with the help of User-Defined Functions (UDFs). CFD simulations are used to recreate phase change experiments from recent studies involving Hydrogen and Methane. Data from the CFD simulations are used to correlate γ to the evaporation rate. A function to calculate γ using the area-averaged phase change molar f (open full item for complete abstract)

Committee: Kishan Bellur Ph.D. (Committee Chair); Prashant Khare Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Fluid Dynamics

Master of Science in Mechanical Engineering (MSME), Wright State University, 2024, Mechanical Engineering

Conventional turbulence models often predict behaviors opposite as to what is observed in flows subject to rotation. In this type of flow scenario, rotation typically induces turbulence suppression. To address this limitation, a modification to the Spalart Allmaras Model with Rotation Correction (SA-R) was proposed to enhance the original Spalart Allmaras Model's sensitivity to rotation and curvature. To test the validity and accuracy of this modification, two cases were investigated. The first case involved an axisymmetric rotating pipe. A Reynolds Number of 37,000 was implemented and the initial and boundary conditions established by Zaets et. al. were utilized. Initially non-rotating, the flow transitioned to full rotation at N=0.6 at 9 m. Results demonstrated strong alignment with experimental data, showcasing improvements over the SA , SA-R, SARC, and SA-R23 models. In the second case, a vortex, surrounded by irrotational flow, was studied. This case used a Reynolds number of 10^5, and implemented the initial and boundary conditions outlined by Spalart and Garbaruk. While the modified model showed improvement over the SA model, it still displayed slight circulation overshoot, a behavior considered unphysical. However, it notably reduced the magnitude of eddy viscosity. The SARC model did produce a laminar state solution. Other vortex parameters also indicated circulation overshoot of the modified SA-R model. Overall, the modified SA-R model showed significant improvement for rotational flow scenarios and holds potential for further refinement to improve accuracy.

Committee: George Huang Ph.D., P.E. (Advisor); José Camberos Ph.D., P.E. (Committee Member); Mitch Wolff Ph.D. (Committee Member) Subjects: Fluid Dynamics

Doctor of Philosophy, The Ohio State University, 2024, Food, Agricultural and Biological Engineering

The smoking process for a food product involves the deposition and absorption of smoke on the product surface, followed by a drying step to reduce the product moisture content to a defined level. The uniformity of air velocity and temperature within a smokehouse significantly influences final product quality, including color, texture, and flavor. Additionally, process efficiency and production capacity depend on uniform heat and mass transfer at the surface for all products in the smokehouse. While Computational Fluid Dynamics (CFD) has been used to study airflow patterns, air velocity and temperature distributions due to ventilation systems, research on applications to airflow distribution in a smokehouse have been limited. The overall objective of this research was to develop and validate CFD simulations of a smokehouse ventilation system to investigate the applications to airflow uniformity within a smokehouse. A CFD simulation of airflow distribution in a smokehouse without product was developed and used to investigate the influence of smokehouse ventilation configuration on uniformity of air velocity. The ventilation system configuration with outlet vents positioned near the inlet vents at both sides of the smokehouse ceiling exhibited the highest air velocity uniformity index of 0.64. An investigation of three different outlet vent dimensions indicated that outlet vent size did not influence the uniformity of air velocity distribution within the empty smokehouse. The influence of model products in the smokehouse was investigated using the CFD simulation. The average air velocity at 20 locations decreased from 3.9 ±1.4 m/s to 2.7 ±0.90 m/s when the ratio of model product to smokehouse volume was increase from 0 to 0.047. The influence of ventilation configuration was also evaluated by comparing outlet vents positioned near the inlet vents at both sides of the smokehouse ceiling to the outlet vent located in the ceiling at the middle of the smokehouse. The ave (open full item for complete abstract)

Committee: Dennis Heldman (Advisor); Sudhir Sastry (Committee Member); Sandip Mazumder (Committee Member); Osvaldo Campanella (Committee Member) Subjects: Engineering; Fluid Dynamics; Food Science

MS, University of Cincinnati, 2023, Engineering and Applied Science: Mechanical Engineering

Bubble dynamics is an integral part of various industrial processes such as aeration, bubble column reactors, and has been a topic of active research for nearly eight decades. Significant progress has been made towards understanding the factors governing the departure bubble size and shape, in particular the effect of liquid physicochemical properties. Bubble dynamics plays an important role in industries such as cosmetics, pharmaceuticals, and paints where a large majority of the liquids being used are of non-Newtonian nature and undergo a change in their viscous properties under the effect of stress. The complex thermo-physical properties of non-Newtonian fluids play a huge role in dictating the bubble growth process and needs further investigation. The aim of this work is to gain a better understanding of the complex physics governing the growth of bubbles from capillary orifices submerged in liquid pools of aqueous solutions of polymers under constant gas flow rate through a combination of experimental and computational approaches. A comprehensive evaluation of existing computational techniques for studying single bubble growth is carried out and coupled level set VOF technique with modifications to the property estimation equation is suggested as a reliable technique to accurately model bubble growth in highly viscous fluids, with large capillary numbers greater than 1. Following this, a brief characterization of non-Newtonian fluids is made along with a comparison of most frequently used rheology models. Selecting the right model plays an important role in computational modeling as each model has its limitations and hence may only be applicable for certain concentrations of polymers. Rupesh Bhatia has shown in his work that the asymptotic forms of certain rheology models work better in characterizing the fluid and the importance of the Asymptotic Power Law (APL) model in the computational modeling of bubble growth in shear-thinning non-Newtonian fluids is esta (open full item for complete abstract)

Committee: Raj Manglik Ph.D. (Committee Chair); Milind Jog Ph.D. (Committee Member); Kishan Bellur Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2023, Engineering and Applied Science: Mechanical Engineering

Wavy fin cores exhibit superior convective heat transfer performance over plain fins due to higher heat transfer surface area, waviness-induced swirl flow, and early inception of turbulence. There is an enhancement of heat transfer in both the laminar and turbulent regimes. In the continuous wavy channel, the waviness causes the flow to recirculate in the trough region, resulting in high local pressures at the flow reattachment locations. In the laminar regime, flow stagnation occurs at the recirculation zone in the trough region, which moderates the increase in heat transfer. In the turbulent regime, the heat transfer is improved because of flow recirculation, which aids in the turbulent mixing of the fluid. In continuous wavy fins, although the convective heat transfer is improved, the associated pressure drop penalty is also considerably higher than the plain fins. In the current study, modified wavy fins such as perforated and slotted wavy fins are investigated to better understand the potential to further improve the performance of wavy fins. The perforated wavy fins are produced through conventional methods of punching holes into aluminum sheet metal and then molding it into a wavy surface. In order to take full advantage of conventional manufacturing techniques, it is beneficial to invest time and resources to examine the performance of perforated wavy fins. A steady, periodically fully developed flow exposed to fin walls with uniform temperature is computationally modeled through perforated wavy fin cores. The computational model is validated by comparing numerical results for pressure drop and heat transfer for continuous wavy fins and perforated wavy fins with available experimental data where excellent agreement is observed. The model is then used to characterize the thermal-hydraulic performance of the air flows (Pr ≈ 0.71 and 50 ≤ Re ≤ 4000) in perforated wavy fin cores. The effect of the number of perforations on the performance of the perforated w (open full item for complete abstract)

Committee: Milind Jog Ph.D. (Committee Chair); Raj Manglik Ph.D. (Committee Member); Je-Hyeong Bahk Ph.D. (Committee Member) Subjects: Mechanical Engineering

PhD, University of Cincinnati, 2023, Engineering and Applied Science: Aerospace Engineering

Boundary layer ingested engines have the potential to offer significantly reduced fuel burn, but the fan stage must be designed to run efficiently with a distorted inflow. It must also be able to withstand unsteady aerodynamic loads resulting from a complex non-uniform flowfield. This research work applies different numerical methods for an improved understanding of the aerodynamic interaction between a transonic fan and inlet distortion. A single stage transonic tail cone thruster fan was designed using both in-house and commercial tools operating in an inlet distortion flowfield. This paper demonstrates that the relevant metrics required to compute the aerodynamic performance of a fan stage in distorted conditions can be reasonably modeled with a few harmonics using the non-linear harmonic method in a fraction of time compared to the full annulus time marching method. The flowfield through a transonic fan/compressor cascade shows a very complex structure due to the presence of shock waves and bladerow trailing edge wakes. In addition, the interaction of these shock waves with the blade boundary layer inherently leads to a very complex flow behavior. The second part of this investigation quantified this behavior and its influence on the stage performance and described the occurring transonic flow phenomena in detail. The last part of this research focussed on detailed unsteady aerodynamic inlet guide vanes (IGV)-Rotor interactions in a single stage transonic fan. In it's first part, the effects of boundary layer ingested inlet distortion on the unsteady flowfield are analyzed on a periodic quarter annulus domain of the IGV-Rotor fan stage, as they result in significant changes in the massflow rate, total pressure ratio and stage isentropic efficiency. The second part assessed the impact of axial IGV-Rotor spacing on the shock wave-boundary layer interaction. It dealt with the unsteady analysis of IGV-Rotor interactions in a single blade passage first stage transo (open full item for complete abstract)

Committee: Mark Turner Sc.D. (Committee Chair); Paul Orkwis Ph.D. (Committee Member); Prashant Khare Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy (PhD), Wright State University, 2023, Engineering PhD

In fluid flow experiments, there have been numerous techniques developed over the years to measure velocity. Most popular techniques are non-intrusive such as particle image velocimetry (PIV), but these techniques are not suitable for all applications. For instance, PIV cannot be used in examining in-vivo measurements since the laser is not able to penetrate through the patient, which is why medical applications typically use X-rays. However, the images obtained from X-rays, in particular digital subtraction angiography, are projective images which compress 3D flow features onto a 2D image. Therefore, when intensity techniques, such as optical flow method (OFM), are applied to these images the accuracy of the velocity measurements suffer from 3D effects. To understand the error introduced in using projective images, a vertical square tube chamber was constructed to achieve various water flow rates with variable dye injection points to perform dye visualization velocimetry (DVV). The results from DVV were compared with PIV measurements to quantify the error associated with DVV. Results from DVV were comparable with PIV, but a machine learning correction method, more specifically multilayer perceptron (MLP), was needed to adjust the DVV results. To train the MLP model, CFD simulations were conducted to generate detailed velocity distributions in the tube and projected dye images which would be used for DVV analysis and thus used as input for training. These CFD simulations were compared with PIV measurements and dye visualization images to validate proper boundary conditions and meshing. For the laminar case, MLP reduces the error associated with DVV from 35% down to 6.9%. When MLP was used to correct instantaneous DVV measurements for the turbulence cases, the error decreased from 22% to 9.8% for measurements 20 mm downstream of the dye inlet. For a time-averaged turbulent case, MLP was able to decrease the v-velocity error down to 5% and reduce the error of DVV by 5 (open full item for complete abstract)

Committee: Zifeng Yang Ph.D. (Advisor); George Huang Ph.D. (Committee Member); Philippe Sucosky Ph.D. (Committee Member); Hamed Attariani Ph.D. (Committee Member); Bryan Ludwig M.D. (Committee Member) Subjects: Engineering; Experiments; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2023, EMC - Mechanical Engineering

In the current study, the quenching and subsequent re-initiation of detonations in irregular premixed hydrocarbon mixtures are investigated using high-resolution numerical simulations. Since appropriate combustion modeling is crucial when simulating the reactive detonation phenomenon, a four-step combustion model is adopted here. First, an investigation of the four-step model is carried out for different reactive mixtures to highlight the model's applicability for detonation applications. In comparison with detailed chemistry mechanisms, the model demonstrates an ability to accurately predict the complete ignition process over a wide range of initial conditions. With the ignition structures and key combustion parameters correctly predicted, it is concluded that the four-step model is an effective and economical tool for studying complex explosion phenomena in situations where pre-combustion temperature and density are constantly changing. In the second half of the study, the four-step combustion model is coupled to an adaptive mesh refinement (AMR)-enabled compressible flow solver to simulate the re-initiation of quenched detonation waves propagating near the critical limit. Two experiments for detonation diffraction and detonation interaction with a single half-cylinder obstacle were successfully simulated. In both cases, the re-initiation of the attenuated detonation was invariably a result of transverse detonation waves. While past attempts using simple chemistry models have failed to capture transverse detonations, for these scenarios, our simulations have demonstrated that the four-step combustion model is able to capture this feature. Thus, it is concluded that to correctly model detonation re-initiation in characteristically unstable mixtures, an applied combustion model should contain at least an adequate description to permit the correct ignition and state variable response when changes in temperature and pressure occur. The re-initiation mechanisms for (open full item for complete abstract)

Committee: Brian Maxwell (Advisor); Shane Parker (Committee Member); Steve Hostler (Committee Member); Bryan Schmidt (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2023, Mechanical Engineering

Since its inception in the 1930s, the evolution of the jet engine has largely been dictated by the need to improve propulsion and fuel economy while reducing noise and environmental impact. Although rapid engineering advancements have enabled progress towards these design objectives, they have also yielded increasingly complex air flowpaths, and further improvements have been inhibited by a lack of understanding of the fluid dynamics. This is because the flowfields are typically characterized by interacting turbulent jets, shear layers, boundary layers, and wakes which evolve in the presence of supersonic expansion and shock waves. Additionally, they are rife with fluid dynamic instabilities that may pose a challenge to the structural, thermal and acoustic performance of the engine. To address this knowledge gap, the present work builds upon a collaborative numerical and experimental campaign between The Ohio State University and Syracuse University, that investigates a supersonic, multistream, airframe-integrated, rectangular nozzle architecture that is representative of emerging industry designs. The configuration consists of a contoured, single-sided expansion nozzle on one side, and a flat aft-deck surface representing the airframe on the other. Within the nozzle, two rectangular streams - a supersonic (Mach 1.6) "core" stream and sonic (Mach 1) "deck" stream - interact after being initially separated by a thick splitter plate. The flow conditions and geometry of the nozzle render a complex 3D flowfield which has been extensively examined in previous work. It is also comprised of a shear layer instability which is initiated at the splitter plate trailing edge (SPTE) and is associated with large vortical structures and a strong tone that have a deleterious effect on the acoustic and structural characteristics of the nozzle. Although previous research works attempting to mitigate the instability by thinning out the SPTE have been promising, such (open full item for complete abstract)

Committee: Datta Gaitonde (Advisor); Jen-Ping Chen (Committee Member); Seung Hyun Kim (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2022, EMC - Aerospace Engineering

Numerical simulations are performed to support a combustion experiment campaign in partial gravity in a centrifuge designed for use in conjunction with the NASA Glenn Research Center's Zero Gravity Research Facility (a 5.2 second drop tower). The centrifuge is a circular dome chamber of volume ~ 0.3 m3 with 81.3 cm diameter. The artificial gravitational field is controlled by the rotation rate of the chamber. This is complicated by gravitational gradients as a function of radius and by Coriolis force as a function of flow velocity. The model is constructed with Ansys FLUENT utilizing a rotating non-inertial reference frame and simulates the entire chamber volume containing a heptane candle with a wick length of 10 mm × 3.18 mm diameter located at 32 cm from the centrifuge center. Simulation results locally near the candle are compared to a series of experiment images where the flame tip bends in the Coriolis force direction. The study investigates the recirculation effects and the relation between the buoyancy and the Coriolis force in how they affect the flame. The model simulates the experiments well and suggestions are made to avoid recirculation effects in future centrifuge experiments.

Committee: Ya-Ting Liao (Committee Chair); Paul Barnhart (Committee Member); Ankit Sharma (Committee Member); Paul Ferkul (Committee Member); Michael Johnston (Committee Member); Bryan Schmidt (Committee Member) Subjects: Aerospace Engineering

Master of Sciences, Case Western Reserve University, 2023, EMC - Aerospace Engineering

Proving the feasibility and overall efficiency of Flapping-Wing Micro Air Vehicles (FWMAVs) over other types of MAVs is vital for their advancement. Due to their complex aerodynamics and the difficulty of building accurate models of the flying animal, assessing the flight performance and efficiency of animals and FWMAVs mimicking those animals can be a challenging task. The research presented here investigates the hawk moth (Manduca Sexta L.) forewing as inspiration for designing an optimal wing for a moth-scale FWMAV using a surrogate modeling approach. The design of experiment (DOE) assesses the variation in aerodynamic lift-to-drag ratio due to variations in the wing geometry parameters. Using results from the experiment as training data, the trained surrogate model is a quadratic Support Vector Regression model that can rapidly evaluate the aerodynamic lift-to-drag ratio based on the wing geometry input parameters, thus identifying local extrema within the design space.

Committee: Kenneth Moses (Committee Chair); Roger Quinn (Committee Member); Bryan Schmidt (Committee Member) Subjects: Aerospace Engineering; Robotics

Doctor of Philosophy, The Ohio State University, 2022, Mechanical Engineering

Downsizing internal combustion engines along with turbocharging is an effective approach in reducing carbon dioxide emissions from vehicles to combat global warming. A turbocharger comprises a radial turbine driven by exhaust enthalpy flow connected on the same shaft to a centrifugal compressor that provides compressed air to the engine. Under certain engine operating conditions, the turbocharger faces challenges, however, due to instabilities encountered by its centrifugal compressor, primarily stall and surge. While stall adversely affects the compressor's aerodynamic performance and efficiency, surge, which is characterized by large amplitude pressure and flow rate fluctuations, results in drastic deterioration of compressor performance and may lead to complete mechanical failure of the turbocharger. The extremely loud noise (reaching 170 dB) generated during surge is also a major concern. To mitigate these instabilities, it is critical to analyze the flow structures involved in these processes. The present work therefore focuses on developing a thorough characterization of the turbocharger compressor flow field over its entire characteristic map (pressure ratio versus flowrate) using state-of-the-art experimental as well as computational techniques. The turbocharger bench stand at OSU-CAR allowed the isolation of the turbocharger's compressor from the complexities of the engine and provided a simplified bench-top environment for studying the compressor instabilities. The facility was modified by incorporating a stereoscopic particle image velocimetry (SPIV) system that facilitated velocity measurements at the compressor inlet. After integrating all the different components of this system including the laser, chiller, cameras, sheet optics, aerosol generator, laser controller, and timing unit, a methodology for stereoscopic calibration, image acquisition, and optimized post-processing was established. Extensive SPIV measurements were then carried out at the c (open full item for complete abstract)

Committee: Ahmet Selamet (Advisor) Subjects: Aerospace Engineering; Automotive Engineering; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2022, EMC - Mechanical Engineering

In this study two models for predicting two-phase configurations are developed and investigated: a theoretical flow boiling critical heat flux (CHF) model and a computational fluid dynamics (CFD) model of a hot reservoir variable conductance heat pipe (VCHP). A new theoretical model for predicting the trigger mechanism for flow boiling CHF is presented. This model incorporates three sub-models: a separated flow model, an interfacial instability model, and a Helmholtz instability model. This study contains comprehensive, consolidated investigations of the flow boiling CHF in single-sided and double-sided heated rectangular channels with subcooled and saturated inlet conditions and in different orientations in Earth gravity and in microgravity. The CHF model captures, in all configurations with good accuracy, low-velocity gravity-dominated flows as well as high-velocity inertia-dominated flows. The model predictions are compared to highly subcooled, slightly subcooled, and saturated two-phase inlet CHF experimental data sets and good agreement is observed evidenced by an overall MAE of 11.07%. A new design for a hot reservoir VCHP is proposed and investigated in this study. In an earlier microgravity test of the hot reservoir design it was found that excessive vapor accumulated in the hot reservoir when the heat pipe started. This phenomenon adversely affects VCHP thermal performance. The only way to remove the excess vapor in the reservoir was by diffusion. However, this process took a long time to complete. A faster way is proposed in this study without affecting the VCHP performance by connecting the non-condensable gas (NCG) section of the heat pipe and the reservoir with an external loop and by placing the NCG pipe inside the VCHP appropriately. A pressure-induced flow is generated through the loop from the NCG section towards the reservoir. A Fortran-based CFD code for VCHP part in conjunction with ANSYS Fluent for the external loop pipe simulation is emplo (open full item for complete abstract)

Committee: Chirag Kharangate (Committee Chair); Yasuhiro Kamotani (Committee Member); Kuan-Lin Lee (Committee Member); Donald Feke (Committee Member); Ya-Ting Liao (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Aerospace Engineering

Rectangular propulsion nozzles offer thrust-vectoring and air-frame-integration advantages over their more commonly studied circular counterparts. However, they display many distinguishing features which violate assumptions, such as azimuthal homogeneity, typically used in acoustic prediction tools for circular jets. In the present work, we examine the turbulent dynamics of rectangular jets from a range of nozzle geometries and operating conditions with the aim of highlighting their distinct nearfield dynamics and developing simplified models for their acoustics. First, the nearfield dynamics of a heated overexpanded rectangular jet of aspect ratio~(AR) two are examined with an implicit Large-Eddy Simulation using experimental data for validation purposes. The conical nozzle, representative of practical configurations, results in multiple shock trains from the throat region as well as the overexpanded operating condition. Each train introduces unsteadiness that influences the external shock cell and plume structure. A detailed analysis of the terms contributing to the turbulent kinetic energy (TKE) is performed to examine the evolution of the plume. The major axis shear layer experiences significant amplification of the TKE compared to the minor axis, particularly near the core-collapse region, and thus, pressure fluctuations in the near acoustic field are correspondingly larger in that direction. The most prominent source of TKE in this region is associated with strong mean flow gradients across the major axis shear layer and larger corresponding cross-correlations of velocity fluctuations. These effects are shown to be consistent with protrusions of vortical perturbations arising in the minor axis shear layer into the potential core. The evolution of pressure perturbations from asymmetric to axisymmetric occurs relatively quickly, to achieve agreement with far-field experimental data. Given the overall similarity of the acoustics from both low AR rectang (open full item for complete abstract)

Committee: Datta Gaitonde (Advisor); Jen-Ping Chen (Committee Member); Mo Samimy (Committee Member) Subjects: Aerospace Engineering